Axial compressors generally are designed to produce a substantially continuous flow of compressed gas or intake air passing therethrough to boost the power of gas turbine engines, such as jet engines for aircraft, high-speed ship engines, as well as some automotive reciprocating engines. In general, most axial compressors will include a series of airfoils, vanes or blades arranged in stages that include pairs of rotating and stationary airfoils. As an air flow enters the inlet of the compressor, the rotating airfoils (rotors) drive the air forwardly through the compressor, increasing the kinetic energy thereof, while the stationary or static airfoils (stators) diffuse the increased kinetic energy of the air flow passing thereover, causing a rise in pressure of the air flow. As a result, the pressure of the axial air flow through the compressor is significantly increased as it passes through multiple stages of the compressor.
However, the pressures and efficiencies provided by axial compressors can be limited by size and weight of the compressor. For example, in military jets where minimizing compressor size and weight is critical to provide a lower profile, higher stage pressure ratios generated by such smaller compressors typically are provided at the expense of reduced compressor efficiency, especially as airflow speeds approach high Mach numbers. Attempts have been made to design compressors with counter-rotation to try to increase the efficiency of axial compressors. The problem with such counter-rotating compressors has traditionally been that the blades of such counter-rotating compressors generally have been required to be on different driveshafts, which adds to the weight and complexity of the compressors, as well as potentially creating problems with synchronizing the operation of the counter-rotating blades, which further increases with an increased number of stages of the compressor.